For cooling an internal combustion engine of an automobile, a cooling circuit has been conventionally used, arranged to cause a coolant fluid, generally water with antifreeze added, to circulate through the engine block in order to absorb its thermal energy and return it to the ambient air by thermal exchange with the air in a heat exchanger, commonly called a cooling radiator.
It is also known to use this coolant in one or more secondary cooling circuits, particularly for cooling the oil lubricating the engine, or to cool the supercharging air coming from a turbocharger. The secondary circuit, or each secondary circuit, then includes a secondary heat exchanger, which is connected in series with the main heat exchanger serving to cool the engine.
This provision is not satisfactory, because thermal antagonisms make it impossible to optimize either the size or the thermal output of the heat exchangers.
In fact, it is necessary for the secondary exchangers to operate at a much lower temperature than the main exchanger serving to cool the engine.
Moreover, the exchanger intended for cooling the supercharging air must operate with relatively low outputs, while the exchanger intended to cool the oil must operate with much higher outputs.
Another reason this known provision is not satisfactory is that it necessitates providing several heat exchangers, thus increasing the size of the engine compartment.
From U.S. Pat. No. 4,535,729, a heat exchanger is also known, arranged to supply two cooling circuits in parallel, one intended for cooling the engine and the other for cooling the oil. To do this, the exchanger includes a fluid tank supplied with the coolant and in turn supplying two heat exchange tube banks, these banks being formed of the same front row of tubes that discharge respectively into two chambers provided longitudinally in a second water tank. These two chambers, separated by a longitudinal partition, supply the cooling circuit for the engine and the the cooling circuit for the oil, respectively.
This apparatus is not satisfactory, because the two banks do not have the same cooling coefficient, because of the fact that the cooling air passes successively through a first and a second layer of tubes. Hence the second layer is cooled by the air that has already been reheated by thermal exchange with the first layer. Moreover, this apparatus cannot be used in the case where the radiator includes only a single row of tubes.
Nor can this exchanger be used for supplying more than two cooling circuits.